The present invention relates to an apparatus for measuring ozone concentration, and more particularly to an apparatus for measuring the concentration of ozone dissolved in a liquid.
A conventional apparatus of the general type to which the invention pertains is shown in FIG. 1.
A pump 1 supplies ozone-containing liquid to a mixing tube 4 at a predetermined constant rate through a pipe 11, and a pump 2 supplies the mixing tube 4 an aqueous solution of potassium iodide at a predetermined constant rate from a tank 3 to be mixed with the ozone-containing liquid.
A photocell 5 receives the mixed liquid from the mixing tube 4. A light source 6 is provided at one side of the photocell 5 for projecting light into the photocell 5 through an optical filter 7. A detector 8 is provided on the side of photocell 5 opposite the light source 6 for detecting or analyzing the concentration of the ozone contained in the mixed liquid. An electrical transmission channel 10 is provided between the detector 8 and a recorder 9 which records the transmitted data.
The operation of the apparatus described above is as follows.
The ozone-containing liquid supplied by pump 1 is uniformly mixed with the potassium iodide (KL) aqueous solution in the mixing tube 4. The ozone contained in the liquid reacts with the potassium iodide (KL) to produce iodine (I.sub.2) according to the reaction: EQU 2KI+O.sub.3 +H.sub.2 O.fwdarw.I.sub.2 +2KOH+O.sub.2.
The iodine (I.sub.2) thus produced has a light absorption spectrum for which the maximum light absorption coefficient occurs in the vicinity of a wavelength of 560 nm. The concentration of the ozone is measured continuously by measuring the amount of light absorption in the vicinity of this wavelength with the photocell 5.
In the conventional type ozone measuring apparatus utilizing the reaction between ozone (O.sub.3) and potassium iodide, when the liquid to be measured contains components other than ozone which can react with potassium iodide (KI) to produce iodine (I.sub.2), for example, oxidizing chlorides (ClO.sup.-, HClO), nitrate ion (NO.sub.3.sup.-), ferric ion (F.sup.3+), etc., it is difficult to measure the concentration of ozone precisely.
In particular, chlorine is usually added as an oxidizer to disinfect ordinary tap water. Consequently, if tap water is used, the influence of chlorine contained therein on the measurement of the concentration of ozone in water or another liquid is unavoidable.